Terrestrial pollen record of recent land-use changes around nine North African lakes in the CASSARINA Project

Pollen analyses and related plant macrofossil records are presented from short cores from nine North African lakes in the EU-funded CASSARINA project. Terrestrial pollen reflects human impact on the vegetation and landscape over the last 150–100 years. Pollen changes, aided by radiometric dating, could be correlated with historical developments. The chronology of the landscape changes date other biostratigraphical records reflecting changes in the aquatic ecosystems.Three lakes in Morocco show gradually intensifying land-use over the last century. Accelerated technological development and landscape modification over the last 20 years culminated in one of the lakes being drained and cultivated during the project period. In Tunisia, a nationally unique acid-water lake is threatened by water withdrawal for increased catchment cultivation. The landscape around two other lakes is being increasingly cultivated and urbanised, and water withdrawal to support this has resulted in deleterious effects on the aquatic ecosystems, particularly at the internationally famous Garaet El Ichkeul where reed-marshes and macrophyte beds have been lost. The three lakes in the Egyptian Nile Delta are in the same hydrological system and show parallel changes in the balance between saltmarsh and reed-marsh. Control of Nile floods and year-round irrigation led to marked increases in cultivation in the delta region since ca. 1920. The Aswan High Dam (1964) had little detectable further effect. Documented planting of dates, palms, and olives and of introduced Casuarina and Eucalyptus trees provided a chronology to supplement the unsatisfactory radiometric dating of the sediments in this low-rainfall area.     

A simple tide simulator for maintenance of marine (intertidal) algal and lichen cultures

Strumpshaw Broad is a medieval man-made lake, excavated about 500 years ago in valley peat deposits. Evidence from diatom fossils, and other remains (filamentous algae, Chrysophycean cysts, sponge spicules, snail shells) indicates a series of changes since the eighteenth century probably related to development of the city of Norwich and sophistications of its sewerage system. Progressive nutrient-enrichment led to replacement around 1912 of low-growing macrophytes (Chara) and sparse plankton populations by tall-growing vascular aquatic macrophytes, with increased epiphytic diatom numbers. A blanketing phase of filamentous algae (probably Vaucheria) was associated with the transition between 1795 and 1903. Around 1950, after a phase of increasing plankton populations and declining epiphyte and macrophyte numbers, the macrophyte-epiphyte complex disappeared altogether, to be replaced by dense plankton populations for a few years. These changes and the progressive decrease in volume of the lake owing to increased build up of sediment throughout the period covered by the core, led to alterations in hydrology which now prevent even plankton development. All data are expressed on absolute bases (amount sedimented per unit area per year) and the necessity for this, as opposed to relative measures (percentage representation, concentration per unit weight) in valid interpretation of palaeolimnological data is emphasized.     

Optimising diquat use for submerged aquatic weed management

An experimentally derived prediction tool is under development which aims to assess potential deactivation of diquat caused by water and deposits on plant leaf surfaces in New Zealand water bodies, where aquatic weeds are targeted for diquat treatment. Optimising the use and success of diquat is important not only in managing public confidence in the use of aquatic herbicides, but also in minimising financial risk from failed treatments. Our approach focuses on characterising lake water quality and plant condition factors in these lakes to identify parameters that might be useful indicators of diquat deactivation potential. Water samples have been collected at 3-month intervals from lakes receiving large scale treatment for weed control. Samples have been analysed for turbidity, suspended solids, chlorophyll a, conductivity and dissolved anions. Samples have also been spiked with 1 mg l⁻¹ diquat to measure loss from adsorption and/or absorption. Shoot samples were also collected from targeted weed species at each sampling site and the amount of organic and inorganic deposits on plants has been measured and then added to a second diquat spiked sample to assess potential additional diquat loss from these deposits. Our results have shown deactivation from deposits on plant surfaces which is highly correlated with turbidity, including inorganic suspended solids and total suspended solids. A plant “dirtiness” scale has been devised to help predict the likely success or risk of diquat failure prior to any decision to proceed with treatment. Deactivation in water was only weakly linked to total suspended solids. Our failure to find significant correlation with the water quality factors measured may reflect the need for more detailed analysis of the particle size and composition of suspended solids and future research will address these issues.     

Dynamics of North Patagonian rainforests from fine‐resolution pollen,charcoal and tree‐ring analysis,Chonos Archipelago,Southern Chile

Abstract Fine‐resolution palaeoecological and dendrochronological methods were used to investigate the impacts of climate change, and natural and anthropogenic disturbances on vegetation in the North Patagonian rainforest of southern Chile at decadal to century timescales during the late Holocene. A lake sediment mud–water interface core was collected from the northern Chonos Archipelago and analysed for pollen and charcoal. Dendrochronological analysis of tree cores collected from stands of Pilgerodendron uviferum close to the lake site was incorporated into the study. The combined analysis showed that the present mosaic of vegetation types in this region is a function of environmental changes across a range of timescales: millennial climate change, more recent natural and anthropogenic disturbances, and possibly short‐term climatic variations. Of particular interest is the spatiotemporal distribution of Pilgerodendron uviferum dieback/burning in the Chonos Archipelago region.     

The dorid nudibranchs Peltodoris lentiginosa and Archidoris odhneri as predators of glass sponges

The dorid nudibranchs Peltodoris lentiginosa and Archidoris odhneri were found on glass sponges (Porifera, Hexactinellida) during remotely operated vehicle surveys of three reefs in the Strait of Georgia, British Columbia, Canada. Eight nudibranchs were sampled from 2009 to 2011. Identification of sponge spicules found in their gut and fecal contents confirmed the nudibranchs to be predators of the reef‐forming hexactinellids Aphrocallistes vastus and Heterochone calyx, as well as of the demosponge Desmacella austini, which encrusts skeletons of the glass sponges. Four of five nudibranchs dissected for gut content analysis had stomachs containing sponge spicules. Counts from high‐definition video footage taken during systematic surveys done in 2009 showed that nudibranchs were found in only two of the three glass sponge reefs. These data provide the first quantitative evidence of a molluscan predator on glass sponges found outside of Antarctica, and establish the first trophic link between glass sponges and their associated community of animals in a sponge reef ecosystem on the western Canadian continental shelf.     

Harnessing the potential of the multi‐indicator palaeoecological approach: an assessment of the nature and causes of ecological change in a eutrophic shallow lake

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The change of sediment composition during recovery of two Finnish lakes induced by waste water purification and lake oxygenation

Total oxygen deficit occurred regularly during stagnation periods in the deepest part of Lake Kallavesi in the period 1973–1986. The sediment was black and anaerobic during the first sampling in 1987. After beginning of artificial lake oxygenation and efficient purification of waste waters of a paper board mill in 1986 the oxygen deficit decreased gradually and a light brown oxidized uppermost sediment layer appeared and began to thicken. The following changes in the sediment composition were observed during 1987–1996: loss on ignition, total nitrogen and BOD₇ concentrations decreased in the uppermost sediment layer (0–2 cm) and BOD₇ concentration increased in the next sediment layer beneath (2–10 cm). There were no significant change in phosphorus and iron concentrations.Lake oxygen, total phosphorus and suspended solids concentrations fluctuated in a noticeable degree in Lake Huruslahti depending on waste water input and artificial oxygenation during the years 1980–1993. Oxygen condition was good at times of successful waste water elimination and lake oxygenation while deterioration of either resulted oxygen deficiency as well as increase of total phosphorus and suspended solids concentration. Most of the internal load entered with suspended solids during periods of total oxygen deficiency.An explanation for the findings in Lake Huruslahti could be microbiological. Gas formation inside sediment lift organic material towards top of the sediment and into the water, but after the lake recovery the material retain in the sediment. Also in Lake Kallavesi microbiological gas formation resuspended sediment particles with phosphorus into the overlaying water prior to oxygenation. During oxygenation microbiological processes in uppermost sediment utilize the anaerobic metabolic products, organic acids and methane, and block gas formation. Organic substances remain in the top sediment decomposing gradually in the uppermost layer.     

Natural and anthropogenic forcing of aquatic macrophyte development in a shallow Danish lake during the last 7000 years

Aim To investigate the long‐term changes in aquatic vegetation in a lowland, shallow lake, and to assess the relationship between aquatic vegetation and natural and anthropogenic catchment changes. Location Gundsømagle Sø, Zealand, Denmark: a shallow (mean depth 1.2 m), hypereutrophic lake (mean annual total phosphorus (TP) c. 700 μg TP L^?1) located in a predominantly agricultural catchment (88% cultivated land). The lake is presently devoid of macrophytes. Methods One hundred and forty‐seven contiguous samples from a sediment core (taken in 2000) were analysed for macrofossil remains together with loss‐on‐ignition and dry weight. From an earlier sediment core (taken in 1992), 67 samples were analysed for pollen and the two cores were correlated using the ignition residue profiles. Core chronology was determined by ²¹⁰Pb and ¹³⁷Cs dating of the recent lake sediments, while older sediments were dated by pollen‐stratigraphical correlation, as ¹⁴C dating proved problematical. Aquatic macrofossil abundance was used to reconstruct past changes in the lake's plant community and water‐level. The contemporary catchment land‐use change was inferred from sedimentary pollen data, and soil erosion to the lake was deduced from the minerogenic content of the lake sediments. Results The macrofossil record covers the last 7000 years, but aquatic plant remains were scarce prior to c. 1300 bc . After this date the abundance of submerged and emergent macrophyte remains increased dramatically, paralleled by an increase in sediment minerogenic matter and non‐arboreal pollen (NAP). Aquatic plant remains were abundant for more than 3000 years until the mid 1900s. Macrofossils of Linum usitatissimum (L.) (flax) and high pollen percentages of ‘Cannabis type’ (hemp) were recorded in periods between c. 1150 bc and 1800 ad . Main conclusions Our study suggests that, between c. 5000 bc and 1300 bc , the submerged plant community was confined to the littoral zone. From 1300 bc onwards, the submerged macrophyte vegetation expanded rapidly across the lake bed, presumably as a response to lake shallowing caused by a combination of climatic‐induced water‐level lowering and enhanced erosional infilling of the lake basin due to intensified anthropogenic activities in the catchment. The lake was meso‐eutrophic and had an extensive and diverse aquatic flora for more than 3000 years, until the middle of the twentieth century. In periods between c. 1150 bc and 1800 ad , the lake experienced direct anthropogenic impact from retting of fibre plants (Linum and Cannabis). Over the last 200 years, erosional infilling of the lake basin increased drastically, probably as a result of agricultural intensification. In the twentieth century, the lake was strongly affected by nutrient enrichment from both point sources (sewage from built‐up areas) and diffuse agricultural run‐off which led to hypertrophic conditions and the collapse of the submerged vegetation c. 1950–60. The concept of ‘naturalness’ and the implications for lake conservation are discussed.     

Resuspension in a shallow eutrophic lake

The frequency and the importance of wind-induced resuspension were studied in the shallow, eutrophic Lake Arresø, Denmark (41 km², mean depth 3 m). During storm events in autumn 1988 lake water samples were collected every 2–8 hours by an automatic sampler at a mid-lake station. The concentration of suspended solids and Tot-P was found to increase markedly. During storms up to 2 cm of the superficial sediment was resuspended, and the concentration of resuspended solids in the water column rose to 140 mg l^–1. The resuspended particles had a relatively high settling velocity and on average, a relatively short residence time in the water column of 7 hours.A model which describes the concentration of resuspended solids as a function of wind velocity and of settling velocity of the resuspended particles is presented. Using additional wind velocity data from a nearby meteorological station, the model has been used to calculate the frequency of resuspension events and concentration of resuspended solids for the period from May to November 1988.These calculations show that resuspension occurred about 50% of the time. Average flux of suspended solids from the sediment to the water was 300 g m^–2 d^–1 and during 50% of the time lake water concentration of suspended solids was more than 32 mg l^–1. A relationship between concentration of suspended solids and Secchi-depth is presented. Because of resuspension, Secchi-depth in Lake Arresø is reduced to 0.5 m.Resuspension also had a marked effect on Tot-P concentration in the lake water, and P input to the lake water being totally dominated by resuspension events.     

Heavy metals (Cu and Zn) in recent sediments of Llangorse Lake,Wales: non-ferrous smelting,Napoleon and the price of wheat — a palaeoecological study

Elevated concentrations of Cu and Zn have been found in the upper part of three sediment cores collected from Llangorse Lake, in south Wales. Palaeomagnetic evidence from one of the cores and ²¹⁰Pb analysis of another, suggests that the increase in sediment Cu and Zn concentrations began during the eighteenth century. A sharp increase in the concentrations of these metals in the sediment profile appears to have occurred during the latter part of the eighteenth century and these concentrations remained high until the mid to late nineteenth century.The absence of known ore deposits and industry around the lake suggests that the lake and catchment soils were increasingly contaminated by long-range aerial transport of emissions from the expanding activity of Cu and Zn smelters located some 80 km upwind in the Swansea area during the Industrial Revolution. Evidence from agricultural crop returns indicates a significant increase in the amount of land devoted to tillage in the catchment, particularly to cereal production, during the late eighteenth and the first half of the nineteenth century which included the Napoleonic Wars. This agricultural shift appears to coincide with increased concentrations of Cu and Zn in the lake sediments. It is suggested that newly ploughed soils, contaminated with metals for many years by long-range aerial transport from the Swansea area, eroded, and were carried into the lake by catchment run-off and added to the sediment burden of Cu and Zn. A subsequent decline of Cu and Zn emissions due to the collapse of the non-ferrous smelting industry and reduced soil erosion because of a 50% reduction of tillage due to an agricultural depression in the second half of the 19th century may explain the fall in Cu and Zn concentrations in the upper part of the sediment profile. The most recent sediments (20th century) show the increase in heavy metals characteristic of many lakes around the world.     

Zooplankton (Cladocera, Ostracoda), Chironomidae and other benthic faunal remains in sediment cores from nine North African wetland lakes: the CASSARINA Project

Palaeolimnological studies were carried out on sediment cores from nine North African wetland lakes. The lakes represented a variety of habitats ranging from freshwater to mixohaline conditions and with and without direct connections to the sea. Sediment cores were examined for records of recent environmental change during the 20th century period. Faunal remains analysed in the sediments included those of Cladocera, Ostracoda, Chironomidae, Mollusca and, at the sites with marine connections, Foraminifera. Cyprideis torosa littoralis was the most common ostracod, occurring in sediments from the seven sites linked with the sea and also in brackish water Sidi Bou Rhaba. In acid Megene Chitane ostracods were scarce, being represented by a single species (Cypria ophtalmica). Candona neglecta completely disappeared at two sites (Sidi Bou Rhaba and Bokka) during the 20th century. Of the Cladocera, Chydorus sphaericus was common in the moderately mixohaline sites and but Heterocypris salina occurred only where marine salinities were occasionally achieved (in Zerga, Ichkeul and Korba). Microinvertebrate assemblages in the Nile Delta lake cores and to a less extent in Zerga showed a clear response indicative of more fresher conditions occurring during the latter part of the 20th century. However the freshening trend began prior to construction of the Aswan High Dam (mid 1960s).With the exception of the most saline site (Korba), microinvertebrate communiuties at all the CASSARINA sites have experienced major disturbances during the 20th century. Changes in freshwater availability associated with increased human usage of water resources is perceived as a major factor regulating the abundance and occurrence of aquatic microinvertebrate species at these sites     

A 25,000-year history for Lake Victoria, East Africa, and some comments on its significance for the evolution of cichlid fishes

SUMMARY. 1. Microfossil and X-ray analyses of sediment cores from Lake Victoria. East Africa, reveal a history of dramatically shifting environmental conditions over the last 25,000 years.
2. The diatom record of a 10 m core collected from beneath 66 m of water at an offshore station extends the known history of the lake 10,000 years beyond the published records from Pilkington Bay and Damba Channel, and shows that maximal late Pleistocene aridity occurred between 15,000 and 13,000 bp . Lack of precipitated carbonates in the offshore sediments suggests that the lake remained relatively dilute throughout the period of record.
3. There is no evidence that the lake level fell low enough to confine fishes to refugia in small isolated ponds or around river mouths.     

Information value of chironomid remains in the uppermost sediment layers of a complex lake basin

The subfossil remains of chironomids were analyzed from four short (35–50 cm) sediment cores in eutrophicated Lake Vanajavesi, southern Finland. The chironomid analysis was found to be a useful palaeolimnological technique for indicating the following aspects: (1) The pollution history of the lake during the last 150 years. A succession from an oligotrophic Micropsectra-Monodiamesa community, through eutrophic Chironomus communities, to the disappearance of the chironomid fauna, was detected. (2) The bottom dynamic conditions at the sampling site. (3) The water level changes of the lake. (4) The significance of bioturbation in the core chronology and stratigraphy. The disappearance of the chironomid remains in the cores was correlated with the occurrence of annually laminated sediment.The most important factor disturbing the interpretation of the cores was the redeposition of head capsules by erosion and transportation. Detailed identification of the remains is necessary to avoid the misinterpretations caused by redeposition. Bioturbation reduces the time resolution of the cores. It is necessary to use dating methods which take the effect of bioturbation into account.     

Sediment resuspension effects on alkaline phosphatase activity

Sediment cores, including the associated lake water, were collected from a shallow hypereutrophic lake located in central Florida. Alkaline phosphatase activity (APA) was measured as an indicator of potential organic P mineralization. In both the sediment and water columns, APA was mainly associated with particulate matter; < 10% of APA was within the soluble phase. This suggests that for enzymatic hydrolysis to occur the hydrolyzable organic compounds must be in close proximity to the particle-bound enzyme complex. Both total P (TP) and APA decreased with depth in the sediment, whereas soluble reactive P increased in the 20–40 cm fraction. Resuspension of surficial sediments resulted in an immediate increase in APA, total suspended solids, TP, total Kjeldahl N, and total organic C within the overlying water column. However, these concentrations decreased rapidly following cessation of turbulence and settling of the sediments, emphasizing the close association of these parameters with the sediment.     

Suspended sediments and nutrients in water ebbing from seagrass-covered and denuded tidal mudflats in a southern Australian embayment

The concentrations of suspended solids, nitrogen (NH₄⁺, NO₃⁻, NO₂⁻), phosphorus (total phosphorus, PO₄⁻³) and silicate were measured in water ebbing from seagrass-covered tidal mudflats and from adjacent ungrassed mudflats in Western Port, Victoria, Australia. Ebb water was collected on six occasions during January and February (summer) and once during July (winter). From both types of mudflats the concentrations of suspended solids, phosphorus and silicate increased during the last hour of ebb tide with maxima in concentrations reached 0.5 to 1 h before slack water ebb. During the last 1.5–2.5 h of ebb tide the suspended solids, phosphorus and silicate concentrations were higher in water ebbing from denuded mudflats than from seagrass-covered mudflats. The concentration of nitrogen remained low in water ebbing from both types of mudflats during the day, but increased significantly during a night-time ebb; light-dependent biological uptake of nitrogen is implicated. It is suggested that denudation of seagrass-covered tidal mudflats would lead to increased efflux of suspended solids, phosphorus and silicate from sediments to overlying water.     

The influence of Corophium volutator abundance on resuspension

Two experiments were performed to test the hypothesis that Corophium volutator affects the turbidity of water in estuaries through active resuspension of sediment. One experiment was done in a flume system under different flow velocities, and one in aquaria. A diatom film developed at the sediment surface in both experiments before Corophium was added. This diatom film was supposed to have a stabilising effect on the sediment. In both experiments, the concentration of suspended solids in the water column increased with the density of Corophium individuals. No effect of flow velocity on suspended solids concentration was found. This indicates that, in our flume experiment, active resuspension by Corophium was more important than physical resuspension, at least at low flow velocity (<20 cm s^-1) and in the presence of a diatom film. The critical erosion threshold decreased with increasing Corophium density in the aquarium experiment, indicating that indirect effects of Corophium grazing may become more important at high levels of bottom shear stress. The implications of our findings for suspended solids concentration in estuarine systems are discussed.     

Ultrastructure of siliceous spicules and microsclerocytes in the marine sponge Neofibularia irata N. SP.

The marine sponge Neofibularia irata contains four different categories of siliceous spicules. These spicules are evident in the tissues as distinct bundles that act to increase the structural rigidity of the sponge. All spicules have a normal structural morphology with silica deposition around a hexagonal axial canal containing a crystalline axial filament. The megasclere strongyles are secreted in typical megasclerocytes. The sigma and raphid microscleres are secreted in individual microsclerocytes that are grouped together in parallel to form loose bundles. However, the microxea microscleres are apparently secreted in distinct tight bundles (trichodragmas) within a single cell. These cells, containing between 13 and 39 spicules, are grouped to form large packets of bundles of spicules.     

Early sponge evolution: A review and phylogenetic framework

Sponges are one of the critical groups in understanding the early evolution of animals. Traditional views of these relationships are currently being challenged by molecular data, but the debate has so far made little use of recent palaeontological advances that provide an independent perspective on deep sponge evolution. This review summarises the available information, particularly where the fossil record reveals extinct character combinations that directly impinge on our understanding of high-level relationships and evolutionary origins. An evolutionary outline is proposed that includes the major early fossil groups, combining the fossil record with molecular phylogenetics. The key points are as follows. (1) Crown-group sponge classes are difficult to recognise in the fossil record, with the exception of demosponges, the origins of which are now becoming clear. (2) Hexactine spicules were present in the stem lineages of Hexactinellida, Demospongiae, Silicea and probably also Calcarea and Porifera; this spicule type is not diagnostic of hexactinellids in the fossil record. (3) Reticulosans form the stem lineage of Silicea, and probably also Porifera. (4) At least some early-branching groups possessed biminerallic spicules of silica (with axial filament) combined with an outer layer of calcite secreted within an organic sheath. (5) Spicules are homologous within Silicea, but also between Silicea and Calcarea, and perhaps with Homoscleromorpha. (6) The last common ancestor of extant sponges was probably a thin-walled, hexactine-bearing sponge with biminerallic spicules. (7) The stem group of sponges included tetraradially-symmetric taxa that grade morphologically into Cambrian fossils described as ctenophores. (8) The protomonaxonid sponges are an early-branching group, probably derived from the poriferan stem lineage, and include the problematic chancelloriids as derived members of the piraniid lineage. (9) There are no definite records of Precambrian sponges: isolated hexactine-like spicules may instead be derived from radiolarians. Early sponges had mineralised skeletons and thus should have a good preservation potential: the lack of sponge fossils in Precambrian strata may be due to genuine absence of sponges. (10) In contrast to molecular clock and biomarker evidence, the fossil record indicates a basal Cambrian diversification of the main sponge lineages, and a clear relationship to ctenophore-like ancestors. Overall, the early sponge fossil record reveals a diverse suite of extinct and surprising character combinations that illustrate the origins of the major lineages; however, there are still unanswered questions that require further detailed studies of the morphology, mineralogy and structure of early sponges.     

Submerged aquatic vegetation correlations with depth and light attenuating materials in a shallow subtropical lake

A 3-year study was done to quantify the biomass of submerged aquatic vegetation (SAV) and its relationship with environmental attributes in Lake Okeechobee, the largest lake in the southeastern United States. Plants were sampled on 21 occasions at sites located along 15 fixed transects around the shoreline, giving rise to 721 observations of SAV species (Chara spp., Vallisneria americana, Hydrilla verticillata, Potamogeton illinoinensis) dry weight biomass. Environmental sampling focused on factors that attenuate light, including phytoplankton chlorophyll a (chl a), total suspended solids (TSS), non-volatile suspended solids (NVSS) and color. Depth and Secchi transparency also were measured. Based on regression analysis, NVSS was considerably more important in attenuating light than chl a or color. Total biomass of SAV varied from 0 to 271 g dw m^–2, with a mean of 4.7 g dw m^–2, and strong dominance by Chara. The SAV biomass was lower than average for Florida lakes, and may reflect the influence of suspended solids on underwater irradiance, as well as high water level in the late 1990s. Dense SAV was found only where depth was < 2 m and TSS < 20–30 mg l^–1. At locations where high biomass of SAV occurred, the plants may have influenced water quality, because concentrations of TSS, NVSS, and chl a were 2–3 fold lower than at sites with no plants. The potential effects of SAV also were apparent at a regional scale. The shoreline region of the lake displayed a pattern of rising and falling chl a and NVSS with water depth. This occurred both at sites with and without plants, suggesting that it may be driven by physical processes, such as water circulation patterns, which are influenced by depth. However, the pattern was dampened at sites with SAV, indicating a potential to influence these attributes of water quality.     

Mesofauna associated with the marine sponge Amphimedon viridis. Do its physical or chemical attributes provide a prospective refuge from fish predation?

Marine sponges often harbor an abundance of associated organisms. We characterized mesofauna associated with the common tropical sponge Amphimedon viridis, and then tested whether physical (spicules) or chemical (lipophilic or hydrophilic extracts) properties of this sponge provide a prospective refuge for mesofauna from fish predation. Sponge analyses revealed a moderately diverse and numerically rich community of sponge-associated mesofauna comprised primarily of mesocrustaceans (82% of total fauna). Eighty-nine percent of these were amphipods, but smaller numbers of tanaids, decapods, and isopods also occurred. Quantitative sampling of outer surfaces and interstices of fifteen A. viridis yielded a total mean ± 1 SD density of sponge–associated mesofauna of 53 ± 9.3 individuals per 100 cm³ wet sponge tissue. Among the numerically dominant amphipods, 65% occurred on outer sponge surfaces where they are most vulnerable to fish predators. We evaluated whether A. viridis provides a prospective refuge from predation by assessing the palatability of this sponge to the sympatric generalist pinfish Lagodon rhomboides. When presented small (2 mm) bite-size pieces of whole sponge tissue, similar in size to what fish might incidentally ingest should they attempt to consume sponge-mesofaunal associates, pinfish displayed strong feeding deterrence. Alginate food pellets containing tissue-level concentrations of sponge spicules caused a weak but significant deterrent response. In contrast, alginate pellets containing tissue-level concentrations of either lipophilic or hydrophilic extracts of A. viridis were highly deterrent to pinfish. Thus, chemical, and to a considerably lesser degree, physical defenses (spicules) may contribute to this sponge serving as a protective refuge for associated mesofauana.